The ESA Earth Explorer 10 candidate satellite mission HARMONY: a focus on ocean submesoscales

The ocean applications of the ESA Earth Explorer 10 candidate satellite mission HARMONY will be presented. The innovative aspect of the mission is the use of a bistatic SAR configuration that will allow the retrieval of the total surface current vector at kilometer or even sub-kilometer scales and of the surface wind vector under all sky conditions. From a user point of view, HARMONY combines the high-resolution provided by imaging radars such as Sentinel-1, with the azimuthal diversity typically encountered in scatterometers. Science questions that could benefit from those measurements will be described, and critical aspects will be discussed. Currently, submesoscale dynamics is studied through models and observed either in-situ during oceanographic campaigns or remotely through the analysis of the evolution of tracers distribution, typically in the visible range and thus available only under clear sky conditions. With this mission, submesoscale dynamics will be observed under all sky conditions, opening up the possibility of gathering information on small scale structures even in high latitude regions. Even at larger scales, the potential of the new measurements will help the community to move beyond the conventional derivation of surface currents from sea surface height data through the assumption of geostrophy. This potentially allows the quantification of surface convergence/divergence with its associated vertical motion in the subsurface. Furthermore, the simultaneous retrieval of surface currents and surface winds opens up the possibility of better knowing the air-sea interaction and the feedbacks between ocean structures and winds. Possible applications to extreme weather events, air-sea interactions, surface convergence/divergence and related vertical motion, tracer transport, ice shelves margins, and coastal dynamics will be presented.